Tires: trailer tires on a E-150 Clubwagon van, maximum inflation, clubwagon

Question
I recently took a trip of over 2,000 miles in my 1995 Ford E-150 Clubwagon; however, although the first 300 miles traveling at 75mph were fine, then upon reaching that first destination, I had a tire shred on a turn at 5mph, front driver side, this tire was over 15 years old, so it's understandable, maybe.  Unable to afford new tires, I pulled into a Used Tire Business, but the only available were ST225/75/15 for trailer use: DOT OU tread-2polyester + 2steel, sidewall 2polyester, weight load D, maximum inflation is for 65psi, but inflated at 45psi.I replaced the two front tires and they are the best looking tires I have ever owned. The tires never felt heated during the trip; at some areas the traffic was 85-90mph. Stopping traction on icy, wet roads was superb. How long can I continue to enjoy these tires?  Should it be better to place on the rear? Do I inflate to maximum or maintain this average 45psi?  
German

Answer
German,

First, I am not a fan of used tires.  You don't know why they are were removed, and that might be important.  Also, unless you know what you are getting, you could get something totally unsuitable - and for some reason, used tire folks seem to be some of the shadiest people.

Second, ST tire were designed to be inexpensive and since they were supposed to be used on trailerss, lower safety standards.  As a result, very few mainline tire manufacturers make them - Too expensive to make them good!

So - I would replace them as soon as possible.  And I mean this week!